Cytochrome p-450 of rat liver metabolized chloramphenicol (CAP) into P-nitro-benzyl alcohol and N-(2-hydroxyethyl)-dichloroacetamide. These products appeared to be formed by the oxidative cleavage of a carbon-carbon bond of CAP. This reaction may represent a previously uncharacterized pathway of metabolism by cytochrome P-450. Under conditions of low oxygen tension, cytochrome P-450 of rat liver catlyzed the dechlorination of CAP to monodeschloro-chloramphenicol. Either monodeshcloro-chloramphenicol or an intermediate produced during its formation appeared to be reactive enough to bind covalently to microsomal protein. Neither chloramphenicol amine nor any other nitro reduction product of CAP was produced by rat microsomes. In contrast, gut bacteria reduced CAP to the amine.